Medea met her husband when Jason and the Argonauts arrived in Colchis to claim the famous Golden Fleece from the king. She fell in love with him and told him she would help him in his quest, under the condition that he would take her with him. Jason accepted and when he presented himself in front of the king, Aeetes agreed to give him the fleece if he passed a number of tasks.

The first task Jason had to complete was to yoke fire-breathing oxen and plough a field with them. To help him, Medea gave him an ointment to apply on himself and his weapons, in order to protect them from the flames. Secondly, he had to take dragon teeth and sow them in the field he had ploughed. No sooner had he sowed them than an army of warriors sprang up. Having been told by Medea, though, Jason was not surprised; he threw a rock amidst the army, and the warriors, not knowing who had thrown the rock, started fighting each other and killed themselves. The third and final task was to kill the sleepless guardian dragon of the Golden Fleece. Medea provided the sleeping herbs with which the dragon fell asleep and Jason then slew him and retrieved the Golden Fleece.

After taking the fleece and sailing away, Jason and Medea were pursued by her father. To slow him down, Medea killed her brother Absyrtus, dismembered him and threw the body parts at sea; her father stopped to gather all the pieces and give his son a proper burial. On the way home, they stopped at Circe's island, Medea's aunt and goddess of magic, in order to absolve Medea of her sin.

They then went near Crete, where Talos, a giant bronze man, guarded the island and threw stones against any ship that approached. Talos had a single vein, through which the blood of the gods, called ichor, flowed. Medea managed to remove the nail which kept the ichor inside, and Talos bled out and died. Landing on Crete, they found out that Jason's father, Aeson, was very ill and old, and Jason asked Medea to help; what she did was to remove the blood of Aeson, infuse it with magical herbs and put it back into his body, reinvigorating him.

Returning to Iolcus, King Pelias' daughters asked Medea to do the same for their father. As Pelias was refusing to give the throne to Jason, Medea thought of making his daughters kill him. She told them that she could restore life by cutting a person in pieces and boiling the parts with herbs. So, the daughters killed their father and threw the body parts in a pot. Thus, this was the ending of a master plan that the goddess Hera had conceived to kill Pelias for being disobedient; it was her who made Jason fall in love with Medea, knowing that she had the power to kill Pelias in the future.

After Pelias' murder, Jason and Medea went to Corinth and had a number of children. Although the myth has different endings, the best known is that Jason abandoned his wife to marry Glauce, the king's daughter. Medea, enraged, sent a dress and a coronet covered in poison, causing the deaths of both Glauce and her father. She then killed her children, and fled to Athens on a golden chariot sent by her grandfather, the god Helios. Afterwards, she went to Thebes where she healed Heracles from a curse that Hera had inflicted on him.

Returning to Athens, she married Aegeus, with whom she had a son, Medus. However, some time later, Theseus, Aegeus' long-lost son, came back to Athens, but father and son did not recognise each other. Medea, though, realised who the newcomer was, and wanting to ensure the kingdom would pass to her own son, tried to poison Theseus. At the very last minute, Aegeus recognised his son by a sword he carried and knocked the cup before Theseus drank the poison.

Finally, there are two versions as to where Medea and her son went after that event. According to one source, she went to modern day Iran, and lived with the locals, who changed their name to the Medes. Another version is that she returned to her homeland, Colchis, where the throne had been usurped by her uncle, Perses. Angry, she killed her uncle and restored her father to the throne.